Pests, such as insect pests, are a major factor in the loss of the world's agricultural crops. For example, corn rootworm and boll weevil damage can be economically devastating to agricultural producers. Insect pest-related agricultural crop loss from corn rootworm alone has reached one billion dollars a year.
Traditionally, the primary methods for controlling insect pests, such as corn rootworm, are crop rotation and application of broad-spectrum, synthetic, chemical pesticides. However, consumers and government regulators alike are becoming increasingly concerned with environmental hazards associated with producing and using chemical pesticides. Because of such concerns, regulators have banned or limited the use of some of the more hazardous chemical pesticides. Thus, there is substantial interest in developing alternatives to chemical pesticides that present a lower risk of pollution and environmental hazards and that provide a greater target specificity than is characteristic of chemical pesticides.
Certain species in the genus Bacillus have polypeptides that possess pesticidal activity against a broad range of insect pests including those in the orders Lepidoptera, Diptera, Coleoptera, Hemiptera and others. For example, Bacillus thuringiensis and Bacillus popilliae are among the most successful species discovered to date having pesticidal activity. Such pesticidal activity also has been attributed to strains of Bacillus larvae, Bacillus lentimorbus, Bacillus sphaericus and Bacillus cereus. See, Biotechnology Handbook 2: Bacillus (Harwood ed., Plenum Press 1989); and Int'l Patent Application Publication No. WO 96/10083.
Pesticidal polypeptides from Bacillus spp. include the crystal (Cry) endotoxins, cytolytic (Cyt) endotoxins, vegetative proteins (VIPs) and the like. See, e.g., Bravo et al. (2007) Toxicon 49:423-435. The Cry endotoxins (also called δ-endotoxins) have been isolated from various strains of B. thuringiensis. A common characteristic of the Cry endotoxins is their expression during the stationary phase of growth, as they generally accumulate in a mother cell compartment to form a crystal inclusion that can account for 23-30% of the dry weight of sporulated cells. The Cry endotoxins initially are produced in an inactive protoxin form, which are proteolytically converted into an active endotoxin through the action of proteases in an insect's gut. Once active, the endotoxins bind to the gut epithelium and form cation-selective channels that cause cell lysis and subsequent death. See, Carroll et al. (1997) J. Invertebr. Pathol. 70:41-49; Oppert (1999) Arch. Insect Biochem. Phys. 42:1-12; and Rukmini et al. (2000) Biochimie 82:109-116.
Although Cry endotoxins often are highly effective against insect pests, some insect pests are not affected by them or show low susceptibility. Likewise, some insect pests have developed resistance to the Cry endotoxins, which threatens their effectiveness. Methods to address these problems include enhancing or expanding Cry endotoxin activity by site-directed mutagenesis, by introducing cleavage sites in specific regions of the endotoxin or by deleting small fragments from the amino-terminus of the endotoxin. See, e.g., Abdullah & Dean (2004) Appl. Environ. Microbiol. 70:3769-3771; Pardo-López et al. (2009) Peptides 30:589-595; Rajamohan et al. (1996) Proc. Natl. Acad. Sci. USA 93:14338-14343; and Wu et al. (2000) FEBS Lett. 473 227-232. These methods, however, can be time consuming and not certain to produce a desired result.
For the foregoing reasons, there is a need for compositions and methods to enhance the pesticidal activity of Cry endotoxins.